dwcaldwell
Looks nice, but there's some wasted space next to the Gain widget.
I was thinking it could contain the missing widgets.

Polarity and Interleave. It might not be the most logical place for them tough... Another option could be a small Input Level Meter! (Then you can see the difference between input and output after the signal has been processed by inserted FX. Could be useful, especially if using hardware inserts).
And how would you customize it so the user could hide any of those widgets?
One obvious answer is to not discard the exiting Volume, Gain and Pan widgets. Call them Compact Volume, Compact Gain, Compact Pan. If anyone wants to use them, go ahead. Then there should be a Compact I/O (just the Input/Output selection above each other). They could even keep the current ones if people prefer those can call them Compact Input and Compact Output. All bases covered.
With the Track Control Manager it should be easy for anyone to add or remove what they want/like.
Just sayin'. 
You are absolutely right, all these kind of things need to be addressed in GUI design.
UnderTow